Ethylene Adsorption on Clean and Oxygen Covered Flat and Stepped Ag(001)

Abstract

In the present paper we review our findings on ethylene adsorption on clean and oxygen covered Ag(001) surfaces investigated by dosing the gas with a Supersonic Molecular Beam and analysing the adsorption state either by High Resolution Electron Energy Loss Spectroscopy or by High Resolution X Rays Photoemission Spectroscopy. The final adsorption state depends on the translational and on the internal energy of the gas-phase molecules and on the presence of defects. At low translational energy ethylene either physisorbs or very weakly chemisorbs at flat terrace sites. The physisorption probability is thereby hindered by rotational excitation. A more strongly bound, π bonded, state forms at higher translational energy, the activation barrier being related to the energy needed to form the relevant defect at which chemisorption takes place. A further even more strongly bound state forms only when dosing vibrationally excited molecules from the gas phase.